I find there is absolutely no grip in the rear of both the XRG and the XRT. I dislike both of them. They drive like none of the other RWD cars in LFS (except maybe XRR I guess, I don't like that car either).
The XFG is the only FWD car that I like to drive. Any other class, I take the RWD over the FWD or AWD. I just enjoy that little hatchback.
Difference between the XF and the XR is, XF will handle the tight corners better, but the XR has better speed on the longer straights. With some tracks that have both tight corners and long straights, it can be a fantastic battle in a mixed field with the XFG taking the insides and carving past in the twisties, only to find the XRG catch on the straights and take it there.
But since the patch and my use of a clutch, it doesn't matter what car I use, I'm getting passed somewhere....